<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
    *{
        margin: 0;
        padding: 0;
    }
    .box{
        width: 100%;
        height: 720px;
        display: flex;
        flex-direction: column;
    }
    .header{
        flex: 2;
        width: 100%;
        background-color: red;
    }
    .content{
        flex: 6;
        width: 100%;
        background-color: blue;
        display: flex;
    }
    .left{
        flex:2;
    }
    .right{
        flex:8;
    }
    .footer{
        flex: 2;
        width: 100%;
        background-color: pink;
    }
    </style>
</head>
<body>
    <div class="box">
        <div class="header">header</div>
        <div class="content">
            <div class="left">left</div>
            <div class="right">right</div>
        </div>
        <div class="footer">footer</div>
    </div>
</body>
</html>